What do you mean you can't? You most certainly can, "just" rewrite the
license to say that redistribution of modified versions is permitted

only it passes QA.

You realise, I am sure, that this "just" would a) require getting the
permission of probably close to 1000 people, almost all of whom are
advocates of free software, and b) not being free software any more. But
I'm sure it wasn't a serious suggestion anyway, so let's not consider it
any more.

The impression you are making here is "Hey, we want to enforce some
limitation, but if we do it through copyright license, we will put
ourselves out of the free software community. So we backdoor the very
same limitation through trademark law in the hope that the free
software community will be confused enough to still count us as a
member, and accept our trojan horse."

Actually, there are free software copyright licences which require a
name change of you make code modifications (e.g. Apache v1). I think
that means that restrictions on names and branding, assuming they don't
present practical difficulties, are certainly not incompatible with free
software.